A technology is known for electronically changing the directivity of an antenna or namely an adaptive array antenna. A common adaptive array antenna is arranged having an array of antenna elements connected to their respective variable amplifiers and variable phase shifters, in which the output signals of the antenna elements can be combined together to develop a composite signal. The antenna directivity can be modified by electronically controlling the action of the variable devices.
Also known is a GPS system for measuring the current position from electric wave signals from two or more satellites. Using the current position of a movable vehicle determined by the GPS system and the position of a broadcasting tower which emits broadcast signals, the positional relationship between the vehicle and the broadcasting tower is calculated and used for aligning the directivity of an adaptive array antenna with the broadcasting tower. As a result, the reception of a desired broadcast signal can be improved while the effect of multi-path interference remaining minimized.
One of the prior art technologies is disclosed as a citation of the present invention in Japanese Patent Laid-open Publication No. (Heisei)11-17433.
The prior art technology is designed for controllably aligning the directivity of an adaptive array antenna with its target broadcasting tower through examining the measurement of a GPS system. However, the prior art technology is feasible only when the environment of broadcast signal reception is as favorable as no interruptions, such as mountains or buildings, between the movable vehicle and the broadcasting tower. Therefore, if any interruption exists between the vehicle and the broadcasting tower, the intensity of a received broadcast signal may not be optimum along the direction extending from the vehicle to the broadcasting tower. Moreover, the prior art technology fails to improve the response to a desired broadcast signal through utilizing reflections of the broadcast signal. Accordingly, the response to a desired broadcast signal will be improved with less certainty.